1. Field of the Invention
The present invention relates to a vibration driven apparatus which clamps an electro-mechanical energy conversion element between first and second elastic vibration members.
2. Related Background Art
As a conventional vibration wave driven apparatus, e.g., an ultrasonic motor, the following two types are known. In one type, a piezoelectric element as an electro-mechanical energy conversion element is joined to one surface of a planar or ring-shaped elastic vibration member using an adhesive, and a driving voltage is applied to the piezoelectric element to generate expansion/contraction in a direction perpendicular to the thickness direction of the piezoelectric element in the elastic vibration member. The expansion/contraction mode is formed to have, e.g., a phase shift of .lambda.(wavelength)/4 to form two phases, i.e., A and B phases, and a travelling wave is formed on the elastic vibration member by synthesizing the two standing waves (U.S. Pat. No. 4,587,452, U.S. Pat. No. 4,587,452, and the like). In the other type, disk-shaped piezoelectric elements are arranged between rod-shaped vibration elastic members in correspondence with, e.g., two phases (A and B phases), and a driving voltage is applied to the piezoelectric elements to generate bending vibrations in the rod-shaped elastic vibration members by expansion/contraction of the piezoelectric elements in their thickness direction. Upon synthesis of the two bending vibrations positionally having a 90.degree. phase shift therebetween, a travelling wave is formed in the driving surfaces of the vibration elastic members (U.S. Ser. No. 008,068, Japanese Laid-Open Patent Application No. 4-91668, and the like). In both types of vibration wave driven apparatuses, an elliptic motion is formed in surface particles of the driving surface on which the travelling wave is formed.
More specifically, the type employing the planar or ring-shaped elastic vibration member utilizes a distortion formed on the elastic vibration member by the expansion/contraction in a direction perpendicular to the thickness direction (to be referred to as an in-plane direction hereinafter) of the piezoelectric element, and forms a vibration (having two or more node diameters) of a wave number of 2 or more on the elastic vibration member.
On the other hand, in the type employing the rod-shaped elastic vibration members, a travelling wave is formed by utilizing bending vibrations produced in a direction perpendicular to the longitudinal direction of a vibration member upon displacement, in the thickness direction (to be referred to as an out-of-plane direction hereinafter), of the piezoelectric elements.
However, the type having the planar or ring-shaped elastic vibration member suffers the following problems.
(1): When the element has a ring shape, a decrease in diameter of the vibration member is limited, and it is difficult to miniaturize the apparatus. PA1 (2): Since vibration in the in-plane direction of the piezoelectric element is used, the frictional driving force factor is small. PA1 (3): Since the piezoelectric element is joined using an adhesive, manufacturing cost increases.
On the other hand, since the type having the rod-shaped vibration elastic members utilizes a bending vibration in the axial direction of a rod-shaped vibration member having an axial length greatly larger than its diameter, the length of the vibration member becomes large.
Applicants'Japanese Laid-Open Patent Application No. 60-170471 relates to the conventional art, wherein two electrostrictive elements are clamped between first and second vibration elastic members.